1. Field of the Invention
The present invention relates to an oil burner for burning a liquid fuel.
2. Description of the Prior Art
Such oil burners have been known as having a combustion chamber defined between a porous inner flame cylinder and a porous outer flame cylinder, the combustion chamber generating a gas of high temperature which red-heats a red-heatable body such as a wire netting, punched metal, metal screen or the like. The oil burner of the kind described, typically oil stoves, are now becoming major household heaters because of various advangages such as elimination of the necessity for electric power supply, small size and light weight which permit easy handling, small possibility of trouble, pleasant feel of heating due to heat radiation and so forth.
The oil burner of the type concerned has a combustion cylinder of a construction which will be described hereinunder with reference to FIG. 1.
A reference numeral 1 designates a wick the lower end of which is immersed in the fuel contained in a fuel tank (not shown) disposed at the lower side thereof, while the upper end is exposed to the combustion chamber. A reference numeral 2 designates an inner flame cylinder, while 3 designates an outer flame cylinder. Both of these cylinders 2 and 3 have numerous apertures formed in their walls. A combustion chamber is formed between the inner flame cylinder 2 and the outer flame cylinder 3. A red-heatable cylinder 4 connected to the upper end of the outer flame cylinder 3 is produced from a metal screen, punched metal, wire netting or the like, and has a porosity greater than that of the outer flame cylinder 3. An outmost cylinder 5 is made of a heat-resistant and light-transmissing material such as a glass, and is held by a metallic cylinder 6. A reference numeral 7 denotes an upper cover connected to the upper end of the inner flame cylinder 2 and having air holes 7a. A flame settling plate 7b is fixed to the upper cover 7.
In the steady state of burning, the liquid fuel is evaporated from the end of the wick to form a fuel gas which is mixed with air supplied by natural draft through the small apertures in the inner and outer flame cylinders 2, 3 and the red-heatable cylinder 4 as well as various openings so that the fuel is partly burnt. The remaining fuel is burnt up by the supply of air (secondary air) through the upper cover 7. This burning system encounters the following problems. Namely, the supply of air (primary air) on the way of flow of the fuel gas to the position of secondary burning (position where secondary air is supplied) is made in quite a dispersed manner through apertures in the inner and outer flame cylinders, so that the concentration of unburnt gas is made smaller at the upper portion of the combustion chamber than at the lower portion of the same. Such uneven concentration distribution makes the perfect burning quite difficult.
To obviate this problem, a method has been adopted in which air is supplied concentrically while forming an adequate concentration of unburnt gas thereby to perfectly burn up the fuel gas in the upper part of the combustion chamber. According to this method, however, the heat produced through the secondary burning does not contribute at all to the red-heating of the red-heatable sleeve 4 so that the ratio of the radiation energy to the fuel consumption is low: namely, the radiation efficiency is impractically low.
When the height of exposed portion of the wick 1 is reduced to decrease the rate of evaporation of the fuel, the degree of red-heating of the red-heatable sleeve 4 is not substantially changed although the flame in the secondary burning region is reduced. This means that the user cannot visually recognize from the appearance of the red-heatable sleeve 4 any reduction of burning rate. In consequence, the user often reduces the exposure height of the wick excessively to cause a burning failure due to excessive air, resulting in the generation of carbon monoxide or offensive odor.